Since morning dew is just condensed water, I doubt it has any special whitening properties.
The sun shining on dewey white clothes might give the impression they are whiter, though.
Here are some tips:
To save on clothespins when hanging bath towels, overlap the corners of bath towels with one another and use one pin to secure the corners to the line. This works with most clothes, but towels are the easiest to learn with.
Hang matching socks together/near each other. When they're done drying, you can pull them off the line and fold them together.
Don't ever yank the clothespinned clothes from the line. This will send clothespins flying into the lawn, and dropped pins and lawnmowers don't mix well.
If you can find wooden clothespins, they work the best (at least in my experience). I prefer the ones that have metal springs; the U-shaped pins limit the size of the clothes that can be attached to the line.
Never hang clothes outdoors if a manure odor is wafting from a nearby farm. Your clothes will smell like manure.
Line-dried towels and jeans can be notoriously scratchy, probably because of the absence of fabric softener (dryer sheets). If you prefer a fluffy towel or softer jeans, make sure to use fabric softener in your washing water.
I think that's about it. You'll do your share of dropping towels into a freshly-cut lawn and having to shake grass clippings out of them until you get the hang of it.
